To a surface of the electrophotographic photosensitive member, an electrical external force and a mechanical external force in charging, cleaning and the like are applied, and therefore the electrophotographic photosensitive member surface is required to have a durability (anti-wearing property) against these external forces.
In order to meet this requirement, such an improving technique that a resin material having a high anti-wearing property has been conventionally used in a surface layer of the electrophotographic photosensitive member.
On the other hand, as a problem generated by enhancing the anti-wearing property of the surface of the electrophotographic photosensitive member, it is possible to cite image deletion (image flow). It would be considered that the image deletion is caused due to deterioration of a material used in the surface layer of the electrophotographic photosensitive member by oxidized gas such as ozone or nitrogen oxide generated by charging of the electrophotographic photosensitive member surface and due to a decrease in resistance of the electrophotographic photosensitive member surface by moisture (water) adsorption. Further, as the anti-wearing property of the electrophotographic photosensitive member surface becomes higher, refreshing (removal of a causative agent (substance) such as a deteriorated material or adsorbed water) on the electrophotographic photosensitive member surface is less liable to be made, and the image deletion is liable to generate.
As a technique for remedying the image deletion, in WO 05/093518 (International Publication No.) publication, a technique for imparting dimple-shaped recessed portions to the electrophotographic photosensitive member surface by dry blasting or wet honing is disclosed. According to WO 05/093518 (International Publication No.) publication, by providing a plurality of the dimple-shaped recessed portions on the surface of the electrophotographic photosensitive member, it is possible to suppress the image deletion from an initial stage to about 5000 sheets.
Further, in Japanese Laid-Open Patent Application (JP-A) Tokkai 2007-233355, a technique for satisfactorily maintaining dot reproducibility from an initial stage to about 5000 sheets even in a high-temperature and high-humidity environment, i.e., for suppressing the image deletion by providing a plurality of recessed portions on the electrophotographic photosensitive member surface at a high area ratio is disclosed.
Further, in JP-A (Tokkai) 2011-22578, a technique in which recessed portions are provided on the electrophotographic photosensitive member surface at a low area ratio is disclosed.
As mentioned above, as the technique for suppressing the image deletion, a technique for providing the plurality of recessed portions on the surface of the electrophotographic photosensitive member has been studied. When the plurality of recessed portions are designed, items such as surface roughness, a size of each of the recessed portions or the number of the recessed portions in a certain area is principally noted.
On the other hand, as a design item of the plurality of recessed portions, there is an item called “arrangement of recessed portions”. In the conventional techniques, although a density of the recessed portions is studied, whether how to arrange the respective recessed portions is not noted.
As a technique noting the arrangement of the recessed portions, in JP-A (Tokkai) 2007-233359, a technique for suppressing growth of damage by arranging the recessed portions within 50 μm of the electrophotographic photosensitive member with respect to a rotational direction of the electrophotographic photosensitive member is disclosed.